Process for sizing cellulose sheets with a starch derivative bearing vicinalglycol groups



United States Patent PROCESS FOR SIZING CELLULOSE SHEETS WITH A STARCI-I DERIVATIVE BEARING VICINAL- GLYCOL GROUPS Hugh J. Roberts, La Grange, and John T. Saatkamp,

La Grange Park, Ill, assignors to Corn Products Company, New York, N.Y., a corporation of Delaware No Drawing. Filed (lot. 24, 1962, Ser. No. 232,864

4 Claims. (Cl. 117-60) This invention relates to a new method of sizing cellulose sheets with starch. More specifically it relates to a novel process wherein paper and paperboard surfaces are pretreated with an aqueous solution of borax (sodium borate), and then sized with a gelatinized starch derivative bearing substituent vicinal (vic.)-glycol groups.

Surface-sizing agents are applied to paper and paperboard for the purpose of improving such properties as printability, abrasive resistance, erasi'bility, and smoothness. Among the materials employed for this purpose are the modified starches and starch derivatives. The Surface size is applied either by tub sizing, that is passing the paper through a water dispersion of the sizing agent, by the use of a size press, or at the calender stack. When the sizing agent is starch, it is customary to apply it in pasted (gelatinized) state so that a film of starch paste is left on the surface of the sheet. Among the advantageous results obtained by surface-sizing are the binding of loose cellulose fibers, the improvement of sheet texture, the tie creased tendency of the paper sheet to curl, the increased resistance to picking during printing, and the increased resistance to penetration by solvents, oils, greases and printing inks.

Although natural starches are sometimes used in surface-sizing, it is usually necessary to reduce the viscosity of the natural starches in order to incorporate into the size a suificient amount of the starch to be effective. Thus, it is common to employ modified starches which possess low viscosities at high concentrations. Methods of modifying starches to obtain the desired low viscosity are well known in the art. These includes dextrinization, acid hdyrolysis, enzyme hydrolysis, and degradative oxidation. Each of these processes results in a decrease in the molecular size of the starch and a consequent reduction in viscosity.

An additional consequence of such modifications of starch :for surface-sizing is increased penetration into the sheet by the smaller starch molecules. Since the effectiveness of a surface size is dependent upon the extent to which the size remains at the surface of the sheet, this increased penetration is undesirable; for with a given amount of size the greater the extent of penetration into the sheet, the smaller is the advantage gained by surfacesizing. With more porous cellulose sheets, such as paperboard, penetration occurs to an even greater extent. Penetration can be reduced by an increase in the viscosity of the size through the use of higher starch concentrations, but this practice is uneconomical. Penetration can also be controlled by varying the time of contact of the paper with the size. In tub sizing the contact time is relatively long and penetration is quite deep. In surface-sizing at the size press or at the calender stack contact time is shorter and less penetration occurs. Even with a relatively short contact time, however, microscopic examination of the cellulose sheet reveals that considerable penetration of the starch occurs.

It is the main object of this invention to provide a process for surface-sizing cellulose sheets with a modified Starch paste in which penetration of the modified starch paste into the sheet is prevented. Another object of the invention is to provide a surface-sizing process in which the amount of starch required is reduced due to the lack of penetration of the starch paste into the sheet. A third object of the invention is to provide a process for imparting to the surface of paper or paperboard markedly increased resistance to penetration of inks, oils and greases. A further object is to provide a process for improving the printability of paper and paperboard. Still another object is to provide a process for imparting a smooth, abrasion resistant finish to the surface of cellulose sheets.

We have discovered that pretreatment of a cellulose sheet with an aqueous solution of borax, followed by surface-sizing the sheet with a starch derivative which carries substituent vie-glycol groups, results in the retention of the size entirely on the surface of the sheet. Particularly suitable for this process are the di- (and poly-) hydroxyalkyl ethers of starch, which may be represented by the formula:

t t R1OCOHZOH wherein R and R are identical preceding formula. be written:

with R and R in the The equation for the reaction may Examples of suitable 2,3-epoxyalcohols are glycidol, 2,3-epoxybutane-1,4-diol, and 2,3-epoxy-2-methylpropa- 1101, which react with starch to form the 2,3-dihydroxypropyl, the 1-hydroxymethyl-2,3-dihydroxypropyl, and the 2-methyl-2,B-dihydroxypropyl ethers of starch, respectively. Other methods of preparing the necessary starch derivatives bearing vie-glycol groups will be evident to those skilled in the art.

It is old in the art to use starch derivatives in the sizing of cellulose surfaces. Specifically, in the commercial manufacture of paper and paperboard it is common to use Z-hydroxyethylated starches. We have found that the use of a starch derivative bearing vie-glycol groups instead of a 2-hydroxyethylated starch to surface-size an untreated cellulose sheet results in a sized sheet having superior surface properties, particularly with reference to inkand oil-holdout. As will be shown in the examples below, little or no improvement in inkand oil-hol-dout properties is obtained 'by pretreatment of the cellulose surface with borax before applying a 2 hydroxyethylated starch. It is a most surprising discovery, then, that an additional and far greater improvement in inkand oil-holdout is obtained by pretreatment of the cellulose sheet with borax, followed by the application of a starch derivative bearing substituent vie-glycol groups.

In explanation of the remarkable inkand oil-holdout properties of paper and paperboard sized by the process of this invention, we believe that a chemical reaction takes place between the 'borax and the vie-glycol groups on the starch derivative to form a cross-linked gel structure. We further believe that this reaction is instantaneous and occurs only at the surface of the cellulose sheet. The crosslinked gel which forms cannot penetrate into the sheet,

and in turn it prevents penetration of any additional size into the sheet. Consequently, all of the size remains on the surface of the sheet to provide a continuous barrier to ink and oil penetration.

Although the starch molecule contains vie-glycol groups, these are in a rigid cyclic configuration, and are incapable of forming the necessary borax complex. On the other hand, the acylic structure of the substituent vie.- glycol groups on the starch derivatives which are essential to the practice of this invention permits the formation of the necessary borax complex.

In the process of this invention the concentration of the borax, Na B O 101-1 0, applied to the cellulose sheet may vary from about 1 percent to that of a saturated solution. However, since the maximum effect appears to be produced when the concentration is 5 percent or greater, a borax concentration of 5 percent is preferred. Because it is the borate ion which is required for the process of this invention, any soluble alkali salt or alkaline earth salt of boric acid may be used. Furthermore, boric acid may replace borax if sufiicient alkalinity is present in, or is added to, the cellulose sheet to convert the boric acid to borate ion.

It is essential to the practice of this invention that the starch used to size the borax pretreated cellulose sheet contain anacyclic vie-glycol group. The linkage between the vie-glycol group and the starch is not critical and may consist of an ether, ester, glycosidic, or direct carbon-carbon linkage. For reasons of economy and stability we have preferred to attach the vie-glycol group to starch through an ether linkage to form derivatives having the generalrformula:

1 Starch-O- wherein R and R are taken from the group consisting,

of hydrogen, alkyl, substituted alkyl, cyloalkyl, alkenyl, aryl and aralky The number of substituent vic.-glycol groups may be between 0.01 and 3.0 per anhydroglucose unit; excellent results, however, are obtained with from 0.1 to 0.2 substituent vie-glycol groups per anhydroglucose residue. Any available starch may be used to prepare the starch derivative, including native starches from corn (maize), potato, wheat, rice, tapioca, sorghum, waxy corn, waxy rice, high amylose corn, etc., and including any of the said native starches which have been modified either by acid hydrolysis, enzyme hydrolysis, oxidation, dextrinization or derivatization, as well as the amylose and amylopectin fractions of said starches.

The invention is illustrated by the following examples which are intended to be informative only and in no way limiting.

EXAMPLE I This example illustrates the resistance to printing ink penetration imparted by a starch glycerol ether (a 2,3- dihydroxypropyl ether of unmodified corn starch), degree of substitution (D.S.) of 0.2, when applied to a borax pretreated cellulose sheet.

Sheets of Whatman No. 1 filter paper were treated as shown in Table I. The sheets were dried in air, conditioned at room temperature and humidity for 24 hours, and then tested for resistance to printing ink by TAPPI Butyl Carbitol Test RG18. The results are shown in Table I.

4 Table 1 .liuie (see) required Treatment for penetration 1 None Impregnated with 5% borax solution No pretreatment, sized with 4% starch glycerol ether paste Impregnated with 5% borax solution,

sized with 4% starch glycerol ether paste 45 1A penetration time of -15 seconds indicates excellent resistance to printing inks.

EXAMPLE II This example illustrates the oil-holdout property imparted to paper by pretreatment with borax followed by sizing with glycerol ethers of acid-modifiedcorn starches.

Pastes containing 6 percent of the corn starch derivatives (60-30 fluidity) listed in Table II were prepared by heating the starch slurries for one-half hour on a steam bath. The pastes were then cooled to F. and applied to 55-pound offset paper with a No. 4 Mayer rod. Half of the paper had been pretreated with a 5 percent solution of borax. The sheets were tested, after condi-- tioning overnight at room temperature and humidity, by measurement of the rate of oil penetration using a Van ceorneter absorption tester (Hillside Laboratory, Chicago, Illinois). The results are shown in Table II together with the values obtained using a commercial Z-hydroxyethylated acid-modified starch.

n Percent Loss in Reflectance is directly proportional to the amount of oil penetration into the sheet.

EXAMPLE III This example illustrates the use of sizes containing corn starch glycerol ethers, acid-modified to a lesser extent than those in Example 11, on borax pretreated paper.

The test was carried out as described in Example II, except that the starches used were in the 20-40 fluidity range. The amounts of oil penetration as measured by percent loss in reflectance are given in Table III together with the values obtained on paper which had not beenpretreated.

Table III Percent Loss in Reflectance No Pretrcat- Borax Pre- Starch Used in Size went treated After After After After 10 secv 50 sec. 10 sec. 50 sec.

Acid-modified 0.10 13.8. starch glycerol ether 20 47 31 31 Acid-modified 018 starch glycerol ether 22 47 16 20 a Percent Loss in Reflectance is directly proportional to the amount of 011 penetration into the sheet.

borax solution and allowed to dry at room temperature overnight. A film, 0.0015-inch thick, of each of the pastes described in Table IV was applied both to the treated and to untreated sheets, and the sheets were again air-dried overnight. The resistance of the sized sheets to penetration by printing ink was determined as in Example I.

The results in Table IV are the average of 15 determinations in each case. The Z-hydroxyethyl starch is typical of some sizes in use in the art, and was included for comparison.

The foregoing tabulated results show that the process for sizing a cellulose sheet consisting of pretreatment of the cellulose sheet with an aqueous solution of borax, followed by the application of a size prepared by pasting a starch derivative carrying a vie-glycol grouping afiords a major increase in the resistance of said sheet to penetration by oils and printing inks.

EXAMPLE V This example illustrates the preparation of l-hydroxymethyl-2,3-dihydroxypropyl starch,

Starch-OCHOHCH2OH HOCHZ 0H To 100 ml. of an aqueous solution containing 13.2 grams of 2,3-epoxyl-1,4-butanediol, 2 grams of Z-butene- 1,4-diol, and 0.7 gram of Na W0 -2H O, prepared from 2-butene-1,4-di0l by a known process (US. 2,833,787), Was added with vigorous agitation 20 grams of Na SO 93 grams of corn starch containing approximately 12 percent H 0, and 21.5 ml. of 1.65 N NaOH. The mixture Was heated with stirring at 50 C. overnight. The resulting slurry was neutralized with 2 N HCl to pH 4.7, filtered, and the cake was washed free from sulfate ions with water and aqueous methanol. The product was further Washed with acetone and dried at 60 C. It contained 0.86 meq. per gram C0H-CH OH, determined by measurement of the HCHO evolved upon oxidation with sodium periodate. This value is equivalent to 0.15

group per anhydroglucose unit. The Scott viscosity was grams per 59 seconds, and the resulting paste was stable but set to a gel upon the addition of borax.

EXAMPLE VI This example illustrates the preparation of Z-methyl- 2,3-dihydroxypropyl starch,

CH3 Starch-0oH( 30Hi0]-1 Example V was repeated using 150 ml. of an aqueous solution containing 15 grams of 2,3-epoxy-2-methylpropanol-l, 7.5 grams of methallyl alcohol, and 1 gram of Na WO -2H O, similarly prepared from methallyl alcohol. At the end of the reaction period the starch had become partially gelatinized and it was necessary to dilute the mixture With water before neutralization. After neutralization to pH 5.7 the slurry was dialyzed against deionized water until free from sulfate ions, and precipitated with methanol containing a small amount of CH CO Na. The precipitate was collected on a filter, washed with methanol and acetone, and dried. It contained 0.98 meq. per gram COHCH OH, equivalent to 0.165

group per anhydrogl-ucose unit. The Scott viscosity was 11 grams per 43 seconds and the resulting paste was stable but gelled upon the addition of borax.

EXAMPLE VII 'This example illustrates the preparation of l-methyl- 2,3-dihydroxypropyl starch,

Example V was repeated using 40 grams of Na SO 43 ml. of 1.65 N NaOH and 200 ml. of an aqueous solution containing 13.5 grams 2,3-epoxybutanol-1, 7.2 grams of 2-butene-1-ol, and 1.6 grams of Na WO -2H O, similarly prepared from Z-butene-l-ol. The product contained 0.15 meq. per gram COHCH OH, equivalent to 0.025

group per anhydroglucose unit, and it had a Scott viscosity of 10 grams per 43 seconds. The paste was stable and became gelatinous upon the addition of borax.

1W8 claim:

1. A process for sizing cellulose sheets which comprises pretreating a cellulose sheet with an aqueous solution of 'borax and then treating said sheet with a gelatinized starch derivative bearing substituent vicinal-glycol groups.

2. The process of claim 1 wherein the starch derivative is the glycerol ether of corn (maize) starch.

3. The process of claim 1 wherein the starch derivative is the 1methyl-2,3-dihydroxypropyl ether of corn (maize) starch.

4. The process of claim 1 wherein the starch derivative is the l-hydroxyrnethyl-Z,3-dihydroxypr0pyl ether of corn (maize) starch.

References Cited in the file of this patent UNITED STATES PATENTS 2,335,126 Lilienfeld Nov. 23, 1943 2,463,869 Hamilton et al. Mar. 8, 1949 3,017,294 Meisel Jan. 16, 1962 3,051,700 lEllZEI et al. Aug. 28, 1962 

1. A PROCESS FOR SIZING CELLULOSE SHEETS WHICH COMPRISES PRETREATING A CELLULOSE SHEET WITH AN AQUEOUS SOLUTION OF BORAX AND THEN TREATING SAID SHEET WITH A GELATINIZED STARCH DERIVATIVE BEARING SUBSTITUENT VICINAL-GLYCOL GROUPS. 